1. Field of the Invention
The present invention concerns karabiners for climbing, potholing and similar activities.
2. Description of the Prior Art
Karabiners normally used at present are in the shape of an elongate closed ring constituted by a generally C-shaped body with the two ends curved towards each other and separated by an opening and a finger articulated at one end to a first end of the body about a transverse axis to pivot in a pivoting plane between an open position pivoted towards the inside of the body and a closed position in which the second end of the finger engages with the second end of the body to close the opening. The respective second ends of the body and of the finger have complementary male and female end shapes adapted to fit one within the other at the end of closing movement in the pivoting plane and to limit outward movement of the finger beyond its closed position so that the karabiner is able to withstand a transverse traction load.
Prior art karabiners are described in documents WO-A-88 03826 and EP-A-0 606 808, for example.
For high resistance to longitudinal traction forces, FIGS. 1 and 2 of document WO-A-88 03826 teach the use of complementary hook shapes, for example a hook shape at the end of the finger or body engaging a crosspiece at the end of the body or finger. These shapes restrict axial separation of the respective second ends of the body and the finger upon deformation of the karabiner body in response to an axial traction load.
However, this hook shape is hazardous in that it can injure the fingers of the user, damage a rope or a strap and impede the insertion of a strap or a rope into or their extraction from the karabiner.
To prevent the hazards associated with the presence of a hook shape of this kind, the other figures of document WO-A-88 03826 and document EP-A-0 606 808 teach a longitudinal T-section body end with two lateral protuberances in a direction perpendicular to the pivoting plane of the finger, said body end engaging with a small clearance in a similar T-shape notch at the end of the finger, the notch having lateral housings in which the lateral protuberances on the body engage when the karabiner is closed. The lateral housings are shaped to oppose any axial relative displacement of the lateral protuberances of the body engaged in the housings, to prevent any axial relative separation of the respective second ends of the body and of the finger when an axial load is applied to the karabiner. At the same time, the lateral housings always allow relative displacement of the protuberances in the finger opening direction.
The prior art also includes lifting hooks as described in EP-A-0 002 396, for example, in which the end of the finger incorporates two lateral branches forming a T-shape, the T-shape end of the finger engaging in a T-shape slot at the end of the hook body.
The devices of documents EP-A-0 606 808, EP-A-0 002 396 and WO-A-88 03826 have the drawback of providing no anti-opening locking action when there is an axial load on the body of the lifting hook.
Providing this anti-opening locking function under load is a problem specific to karabiners used for climbing and potholing, since there is a risk of the karabiner opening when inserted in a piton or other roping device ring if the finger is near a wall, for example: if the forces on the ropes in the karabiner force the finger against the wall, it is pushed in the opening direction, i.e. towards the interior of the karabiner; when the finger pivots towards the open position, it no longer contributes to withstanding axial loads, which are taken only by the body of the karabiner, which in turn reduces the load capacity of the karabiner. It is therefore beneficial to prevent the karabiner finger opening in this way, especially if an axial traction load is applied to the karabiner body.
The problem addressed by the present invention is that of designing a new karabiner which, whilst avoiding the use of a hazardous hook part, combines good axial load strength with anti-opening locking under load.
Another requirement is to increase the mechanical strength of the karabiner without increasing its weight.
The solution of the invention must be compatible with a karabiner body and finger having a substantially constant transverse cross-section, as in karabiners used for climbing and potholing, to enable the karabiner to turn easily in the ring of a piton or other roping device.
The karabiner of the invention must additionally be easy to manufacture by means of simple machining operations.